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Z. J. Yu, C. T. Russell, M. G. Kivelson, K. K. Khurana (Institute of Geophysics and Planetary Physics, University of California Los Angeles)
Massloading of the jovian magnetosphere by the addition of ions at the moon Io is the ultimate engine of the circulation of the magnetospheric plasma. In steady state the radial density profile enables the radial outflow velocity to be calculated from the mass addition rate. Some of these ions are lost from the field lines through pitch angle diffusion. Expected loss rates can be calculated from the fluctuation level in the magnetic field. Radial velocities can be calculated from observations of the Europa wake and force balance in the magnetodisk. The resulting transport times are shorter than the pitch angle scattering loss times so that most of the plasma is transported to the tail and lost by magnetic island formation. In turn the island formation process (reconnection) depletes magnetic field lines making them buoyant and allowing them to "float" back to the inner magnetosphere. In the torus these depleted flux tubes can be seen as thin tubes with stronger than the ambient field strength, implying plasma pressures about 2% of the magnetic field and ion temperatures principally in the range 30-150 eV. When the depleted flux tubes reach the orbit of Io where the energy density of the plasma drops these depleted flux tubes become indistinguishable from the ambient plasma, completing the circulation loop.